JP4939360B2 - Group III nitride crystal growth method - Google Patents

Description

  The present invention relates to a method for growing a group III nitride crystal by a liquid phase method.

  Group III nitride crystals are widely used for substrates of various semiconductor devices. In recent years, in order to efficiently manufacture various semiconductor devices, a large group III nitride crystal has been demanded.

  As a method for growing a group III nitride crystal, there are a gas phase method such as HVPE (hydride vapor phase epitaxy) method and MOCVD (metal organic chemical vapor deposition) method, a liquid phase method such as solution method and flux method. . Here, the liquid phase method is superior to the gas phase method in terms of environmental protection because no toxic gas is used in crystal growth.

  For example, M. Bockowski, “Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure”, Cryst. Res. Technol., Vol. 36, (2001) , 8-10, p. 771-787 (Non-Patent Document 1) discloses a method for growing GaN crystals by a high-pressure solution method. H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol. 9, No. 2, (1997), p. 413-416 (Non-patent Document 2) Discloses a method for growing GaN crystals by the Na flux method. Japanese Patent Laying-Open No. 2003-206198 (Patent Document 1) discloses a GaN crystal growth method using a plate-like group III nitride seed crystal by the Na flux method.

However, the growth method disclosed in Non-Patent Document 1 increases the manufacturing cost of crystals because the crystal growth conditions are 1 GPa and 1 GPa at 1500 ° C., and grows large crystals because seed crystals are not used. Is difficult. The growth method disclosed in Non-Patent Document 2 is a crystal growth condition that is relatively easy to carry out at 800 ° C. and 10 MPa, but it is difficult to grow a large crystal because no seed crystal is used. Moreover, since the diameter of the plate-shaped seed crystal used in the growth method disclosed in Patent Document 1 is not large, large crystals are not obtained.
JP 2003-206198 A M. Bockowski, “Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure”, Cryst. Res. Technol., Vol.36, (2001), 8-10, p.771-787 H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol. 9, No. 2, (1997), p.413-416

  However, in the growth of a group III nitride crystal by a liquid phase method such as a solution method or a flux method, a group III nitride crystal having the same chemical composition as the substrate is formed on a large-diameter plate-like group III nitride crystal substrate. Even with homoepitaxial growth, cracks occur in the substrate and the group III nitride crystal grown on the substrate, and it is difficult to obtain a large group III nitride crystal substrate.

  An object of this invention is to provide the growth method of the group III nitride crystal which can grow a large crystal | crystallization in a liquid phase method.

  As a result of examining the cause of the cracks of the group III nitride crystal substrate and the group III nitride crystal in detail, it was found that there is a correlation between the cracks of the substrate and the group III nitride crystal and the thickness of the substrate. Further, by proceeding with the study, in the homoepitaxial growth of the group III nitride crystal on the group III nitride crystal substrate by the liquid phase method, the thickness of the group III nitride crystal substrate is 0.5 mm or more, preferably 0.67 mm. As described above, more preferably 0.84 mm or more, and even more preferably 1.0 mm or more, the cracks of the group III nitride crystal substrate and the group III nitride crystal grown thereon are suppressed, and a large group III It has been found that nitride crystals can be grown.

The present invention relates to a growing method of a group III nitride crystal by liquid phase method, a group III have the same chemical composition as the nitride crystal and 1.0mm or 2.0mm thickness less than the chromatic vital principal surface solution but with a step of preparing a III nitride crystal substrate to have a 20 cm ² or more areas, on the main surface of the group III nitride crystal substrate by dissolving the nitrogen-containing gas in a solvent containing a group III metal and an alkali metal And a step of growing a group III nitride crystal on the main surface, wherein the solvent contains a group III metal having a purity of 99 mol% or more and an alkali metal having a purity of 99 mol% or more This is a method for growing a nitride crystal.

In the growing method of a group III nitride crystal according to the present invention, nitrogen-containing gas may be pure to 99 mol% or more nitrogen gas.

  ADVANTAGE OF THE INVENTION According to this invention, the growth method of the group III nitride crystal | crystallization which can suppress generation | occurrence | production of a crack in a liquid phase method and can grow a large crystal | crystallization is provided.

  One embodiment of a method for growing a group III nitride crystal according to the present invention is a method for growing a group III nitride crystal 10 by a liquid phase method with reference to FIG. A step of preparing a group III nitride crystal substrate 1 having a chemical composition and a thickness of 0.5 mm or more, and a solvent containing a group III metal and an alkali metal on the main surface 1m of the group III nitride crystal substrate 1 And a step of growing a group III nitride crystal 10 on a main surface 1 m by bringing a solution in which a nitrogen-containing gas 5 is dissolved into contact with 3 to form a group III nitride crystal.

  According to the method for growing a group III nitride crystal of the present embodiment, generation of cracks in the group III nitride crystal substrate and the group III nitride crystal grown on the main surface of the substrate is suppressed, and a large group III A nitride crystal is obtained.

  The growth method of the group III nitride crystal of this embodiment is a growth method of the group III nitride crystal 10 by a liquid phase method. Here, the liquid phase method refers to a method of growing crystals in the liquid phase.

The group III nitride crystal growth method of the present embodiment is a step of preparing a group III nitride crystal substrate 1 having the same chemical composition as the group III nitride crystal 10 to be grown and having a thickness of 0.5 mm or more. Is provided. Since group III nitride crystal substrate 1 has the same chemical composition as the group III nitride crystal to be grown, group III nitride crystal 10 is homoepitaxially grown on main surface 1 m of group III nitride crystal substrate 1. Can do. For example, when an Al _x Ga _y In _1-xy N crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is homoepitaxially grown as the group III nitride crystal 10, the group III nitride crystal substrate 1 is made of Al _x. A Ga _y In _1-xy N crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is used.

  Further, since group III nitride crystal substrate 1 has a thickness of 0.5 mm or more, it is between group III nitride crystal substrate 1 and group III nitride crystal 10 grown on its main surface 1 m. Generation of cracks due to the generated stress can be suppressed by the rigidity of the group III nitride crystal substrate 1. From such a viewpoint, the group III nitride crystal substrate 1 preferably has a thickness of 0.67 mm or more, more preferably 0.84 mm or more, and 1.0 mm or more. More preferably, the thickness is as follows. On the other hand, since the group III nitride crystal substrate is expensive, the thickness of the substrate is preferably as small as possible from the viewpoint of cost. For example, the group III nitride crystal substrate preferably has a thickness of 2.0 mm or less.

It principal surface area of 1m of the III-nitride crystal substrate 1 is not particularly limited, it is preferably 0.78 cm ² or more, more preferably 5 cm ² or more, 20 cm ² or more Is more preferable. In the growth of the group III nitride crystal 10 in the growth method of the present embodiment, even if the area of the main surface 1m of the group III nitride crystal substrate 1 increases, the group III nitride crystal substrate 1 and the group III nitride crystal 10 can be prevented from cracking.

  Here, the group III nitride crystal substrate 1 used in the present embodiment is particularly limited as long as it has the same chemical composition as the group III nitride crystal 10 to be grown and has a thickness of 0.5 mm or more. Even if it is grown by a liquid phase method such as a solution method or a flux method, the HVPE (hydride vapor phase epitaxy) method, the MOCVD (metal organic chemical vapor deposition) method, the MBE (molecular beam growth) method, etc. It may be grown by the vapor phase method. From the viewpoint of easily obtaining thick crystals, those grown by the HVPE method are preferred.

  In the method for growing a group III nitride crystal according to the present embodiment, a solution obtained by dissolving a nitrogen-containing gas 5 in a solvent 3 containing a group III metal and an alkali metal is brought into contact with the main surface 1 m of the group III nitride crystal substrate 1. And a step of growing the group III nitride crystal 10 on the main surface 1 m. By providing the growth process of the group III nitride crystal 10, it is possible to suppress the generation of cracks in the group III nitride crystal substrate 1 and the group III nitride crystal 10 grown on the substrate.

  The growth process of group III nitride crystal 10 is performed, for example, as follows. First, the group III nitride crystal substrate 1 is placed in the crystal growth vessel 23 with its main surface 1 m facing upward, and the solvent 3 containing a group III metal and an alkali metal is placed. This solvent 3 is solid at room temperature (about 25 ° C.), but is liquefied by subsequent heating.

  Although there is no restriction | limiting in particular in the solvent 3 containing a III group metal and an alkali metal, From the viewpoint of growing the high purity group III nitride crystal | crystallization 10, the thing with the high purity of a group III metal and an alkali metal is preferable. From this viewpoint, the solvent 3 preferably contains a Group III metal having a purity of 99 mol% or more and an alkali metal having a purity of 99 mol% or more, and has a 99.999 mol% or more Group III metal and 99.999 mol. It is more preferable to contain at least% alkali metal. Here, when the solvent 3 contains two or more group III metals, the purity of each group III metal is preferably 99 mol% or more, more preferably 99.999 mol% or more. . Moreover, when the solvent 3 contains 2 or more types of alkali metals, it is preferable that each purity of each alkali metal is 99 mol% or more, and it is more preferable that it is 99.999 mol% or more.

  When the solvent 3 containing a Group III metal and an alkali metal is used, the concentration of impurities including the Group III metal (for example, a concentration of less than 1 mol% with respect to the whole solvent) or higher is used compared to the case of using a solvent containing no alkali metal It is possible to reduce the growth temperature and pressure of the group III nitride crystal and increase the crystal growth rate. This is presumably because the alkali metal contained in the solvent 3 promotes the dissolution of the nitrogen-containing material 5 in the solvent 3.

The molar ratio of the Group III metal M _III an alkali metal M _A contained in the solvent 3 is not particularly limited, the growth temperature of the group III nitride crystal, to reduce the growth pressure, in view of enhancing the crystal growth rate, M _III : M _A = 90: 10 to 10:90 is preferable, and M _III : M _A = 50: 50 to 20:80 is more preferable. Even if the molar ratio of the group III metal M _III is larger than M _III : M _A = 90: 10 or the molar ratio of the alkali metal M _A is larger than M _III : M _A = 10: 90, the crystal growth rate decreases. To do.

  Further, the amount of the solvent 3 containing the group III metal and the alkali metal put in the crystal growth vessel 23 is not particularly limited, but the depth of the liquefied solvent 3 (melt) is determined from the surface of the solvent 3 to group III nitridation. The main surface of the physical crystal substrate 1 is preferably 1 mm or more and 50 mm or less up to 1 m. If the depth is less than 1 mm, the main surface 1 m of the group III nitride crystal substrate 1 may not be covered with the solvent 3 (melt) due to the surface tension of the solvent 3. This is because the supply of nitrogen is insufficient.

  Next, the crystal growth vessel 23 in which the group III nitride crystal substrate 1 and the solvent 3 containing a group III metal and an alkali metal are arranged is heated, and the nitrogen-containing gas 5 is introduced into the solvent 3 in the crystal growth vessel 23. The temperature in the crystal growth vessel 23 (crystal growth temperature) is 750 to 900 ° C., and the pressure of the nitrogen-containing gas in the crystal growth vessel 23 (crystal growth pressure) is 2 MPa to 5 MPa. At this time, the solvent 3 containing a Group III metal and an alkali metal is liquefied, and the nitrogen-containing gas 5 is dissolved in the liquefied solvent 3. In this way, a solution in which the nitrogen-containing gas 5 is dissolved in the solvent 3 containing a group III metal can be brought into contact with the main surface 1m of the group III nitride crystal substrate 1, and the group III nitride crystal is formed on the main surface 1m. 10 grows.

  The nitrogen-containing gas 5 is not particularly limited, but from the viewpoint of growing a high purity group III nitride crystal 10, a nitrogen gas having a purity of 99 mol% or more is preferable, and a nitrogen having a purity of 99.999 mol% or more is preferable. More preferably, it is a gas.

  Next, after the group III nitride crystal 10 is grown, the temperature and pressure in the crystal growth vessel 23 are lowered to room temperature and atmospheric pressure, and then the group III nitride grown on the group III nitride crystal substrate 1 is grown. The product crystal 10 is removed from the solvent 3. Even when stress is applied between the group III nitride crystal substrate 1 and the group III nitride crystal 10 during crystal growth and when the temperature and pressure in the crystal growth vessel 23 are lowered later, the thickness is 0.5 mm or more. Due to the rigidity of group III nitride crystal substrate 1 having a thickness, generation of cracks in group III nitride crystal substrate 1 and group III nitride crystal 10 is suppressed.

( Reference Example 1)
Referring to FIG. 1, as a group III nitride crystal 1, a GaN bulk crystal grown by the HVPE method is sliced in a plane parallel to the (0001) plane, and its main surface 1m ((0001) surface) is polished. A GaN substrate having a diameter of 2 inches (5.08 cm) and a thickness of 0.5 mm was prepared. The area of the main surface 1 m of the GaN substrate was 20 cm ² .

Next, in the crystal growth vessel 23, a GaN substrate (Group III nitride crystal substrate 1), metal Ga having a purity of 99.9999 mol% and metal Na (solvent 3) having a purity of 99.9999 mol% are placed. Arranged. Here, the metal Ga (group III metal M _III ) and the metal Na (alkali metal M _A ) were made to have a molar ratio of M _III : M _A = 30: 70. Next, the inside of the crystal growth vessel 23 was evacuated (vacuum degree: 1 × 10 ⁻³ Pa).

  Next, nitrogen gas (nitrogen-containing gas 5) having a purity of 99.99999 mol% was supplied into the crystal growth vessel 23 so that the pressure in the crystal growth vessel became 1 MPa. Next, the crystal growth vessel 23 was heated to raise the temperature in the crystal growth vessel 23 to 850 ° C. At this time, metal Ga and metal Na are liquefied to form a Ga—Na melt (solvent 3), and the depth of the Ga—Na melt (solvent 3) is from the surface of the melt to the main surface 1 m of the GaN substrate. It was 5 mm.

  Next, nitrogen gas (nitrogen-containing gas 5) having a purity of 99.99999 mol% is further supplied into the crystal growth vessel 23 while maintaining the temperature in the crystal growth vessel 23 at 850 ° C. Was increased to 3 MPa. At this time, nitrogen gas (nitrogen-containing gas 5) is dissolved in the Ga—Na melt (solvent 3) to form a solution in contact with the main surface of the GaN substrate.

  Next, a GaN crystal (III) on the main surface 1 m of the GaN substrate at a crystal growth temperature (temperature in the crystal growth container at the time of crystal growth) 850 ° C. and crystal growth pressure (pressure in the crystal growth container at the time of crystal growth) 3 MPa. Group nitride crystals 10) were grown to a thickness of 0.5 mm.

The growth of the GaN crystal was performed 10 times, and the ratio of the samples in which cracks occurred in at least one of the GaN substrate and the GaN crystal in the sample composed of 10 GaN substrates and Ga crystals was calculated as the crack occurrence rate (%). . The crack occurrence rate in Reference Example 1 was 70%. Here, if the crack occurrence rate is 70% or less, the minimum reproducibility necessary for the production can be ensured, and the GaN crystal can be produced by this production method. The results are summarized in Table 1.

(Example 2)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Reference Example 1, except that a GaN substrate (Group III nitride crystal substrate 1) having a thickness of 1.0 mm was used. The crack occurrence rate in Example 2 could be as low as 10%. The results are summarized in Table 1.

(Example 3)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Reference Example 1 except that a GaN substrate (Group III nitride crystal substrate 1) having a thickness of 1.3 mm was used. The crack occurrence rate in Example 3 was 0%, and the occurrence of cracks could be completely suppressed. The results are summarized in Table 1.

(Comparative Example 1)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that a GaN substrate (Group III nitride crystal substrate 1) having a thickness of 0.35 mm was used. The crack occurrence rate in Comparative Example 1 was as high as 90%. The results are summarized in Table 1. The relationship between the substrate thickness and the crack generation rate is shown in FIG.

  As is apparent from Table 1, the GaN crystal (Group III nitride crystal 10) is cracked on the main surface of the GaN substrate (Group III nitride crystal substrate 1) having a thickness of 0.5 mm or more by the liquid phase method. It can be grown at an incidence of 70% or less. Further, as is apparent from FIG. 2, a GaN substrate having a thickness of 0.5 mm or more is necessary to reduce the crack occurrence rate to 70% or less, and 0% to reduce the crack occurrence rate to 50% or less. A GaN substrate of .67 mm or more is required, a GaN substrate of 0.84 mm or more is required to reduce the crack generation rate to 30% or less, and 1.0 mm to reduce the crack generation rate to 10% or less. It can be seen that the above GaN substrate is necessary. Therefore, the thickness of the group III nitride crystal substrate is required to be 0.5 mm or more, preferably 0.67 mm or more, more preferably 0.84 mm or more, and further preferably 1.0 mm or more.

( Reference Example 4)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that a GaN substrate (Group III nitride crystal substrate 1) having a diameter of 1.0 cm was used. Here, the area of the main surface of the GaN substrate used in Reference Example 4 was 0.78 cm ² . The crack occurrence rate in Reference Example 4 was as low as 10%. The results are summarized in Table 2.

( Reference Example 5)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that a GaN substrate (Group III nitride crystal substrate 1) having a diameter of 1.8 cm was used. Here, the area of the main surface of the GaN substrate used in Reference Example 5 was 2.54 cm ² . The crack occurrence rate in Reference Example 5 could be as low as 10%. The results are summarized in Table 2.

( Reference Example 6)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that a GaN substrate (Group III nitride crystal substrate 1) having a diameter of 1 inch (2.54 cm) was used. Here, the area of the main surface of the GaN substrate used in Reference Example 6 was 5 cm ² . The crack occurrence rate in Reference Example 6 was as low as 10%. The results are summarized in Table 2. In Table 2, Example 2 is also summarized for comparison.

  As can be seen from Table 2, if the thickness of the GaN substrate (group III nitride crystal substrate 1) is the same, the same crack occurrence rate can be obtained even if the area of the main surface of the GaN substrate is different. . That is, it can be seen that by using a group III nitride crystal substrate having a thickness of 0.5 mm or more and a large principal surface area, a large group III nitride crystal can be grown with a low crack generation rate.

(Example 7)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that the GaN crystal (Group III nitride crystal 10) was grown to a thickness of 0.01 mm. The crack occurrence rate in Example 7 could be as low as 10%. The results are summarized in Table 3.

(Example 8)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that the GaN crystal (Group III nitride crystal 10) was grown to a thickness of 1.0 mm. The crack occurrence rate in Example 8 could be as low as 10%. The results are summarized in Table 3.

Example 9
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 2 except that the GaN crystal (Group III nitride crystal 10) was grown to a thickness of 2.0 mm. The crack occurrence rate in Example 9 could be as low as 10%. The results are summarized in Table 3. In Table 3, Example 2 is also summarized for comparison.

  As is apparent from Table 3, if the thickness of the GaN substrate (group III nitride crystal substrate 1) is the same, the same crack occurrence rate can be obtained even if the thickness of the GaN crystal to be grown is different. . That is, it can be seen that group III nitride crystals of various thicknesses can be grown with a low crack generation rate by using a group III nitride crystal substrate having a major surface area of 0.5 mm or more in thickness. .

(Example 10)
The GaN crystal (Group III nitride crystal 10) was formed in the same manner as in Example 2 except that the crystal growth temperature for growing the GaN crystal (Group III nitride crystal 10) was 800 ° C. and the crystal growth pressure was 2 MPa. Grown up. The crack occurrence rate in Example 10 was as low as 10%. The results are summarized in Table 4.

(Example 11)
The GaN crystal (Group III nitride crystal 10) was formed in the same manner as in Example 2 except that the crystal growth temperature for growing the GaN crystal (Group III nitride crystal 10) was 870 ° C. and the crystal growth pressure was 4 MPa. Grown up. The crack occurrence rate in Example 11 was as low as 10%. The results are summarized in Table 4.

(Example 12)
A GaN crystal (Group III nitride crystal 10) is formed in the same manner as in Example 2 except that the crystal growth temperature for growing the GaN crystal (Group III nitride crystal 10) is 900 ° C. and the crystal growth pressure is 5 MPa. Grown up. The crack occurrence rate in Example 12 was as low as 10%. The results are summarized in Table 4. In Table 4, Example 2 is also summarized for comparison.

  As can be seen from Table 4, if the thickness of the GaN substrate (group III nitride crystal substrate 1) is the same, the same crack generation rate can be obtained even if the growth conditions of the GaN crystal are different. That is, by using a group III nitride crystal substrate having a major surface area of 0.5 mm or more and a large area, a group III nitride crystal can be grown with a low crack generation rate even under various crystal growth conditions. I understand.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Group III nitride crystals obtained by the growth method according to the present invention include light-emitting elements such as light-emitting diodes and laser diodes, electronic elements such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (high electron mobility transistors), temperature For sensors, pressure sensors, radiation sensors, semiconductor sensors such as visible-ultraviolet light detection, SAW devices (surface acoustic wave elements), vibrators, resonators, oscillators, MEMS (microelectromechanical system) components, piezoelectric actuators, etc. It is used for the substrate.

It is a schematic sectional drawing which shows one Embodiment of the growth method of the group III nitride crystal concerning this invention. It is a graph which shows the relationship between the thickness of a board | substrate, and a crack generation rate.

Explanation of symbols

  1 Group III nitride crystal substrate, 1 m main surface, 3 solvent, 5 nitrogen-containing gas, 10 Group III nitride crystal, 23 crystal growth apparatus.

Claims (2)

A method for growing a group III nitride crystal by a liquid phase method,
Preparing a III nitride crystal substrate on which the Group III have the same chemical composition as the nitride crystal and 2.0mm or less in thickness Yu vital principal surface than 1.0mm to have a 20 cm ² or more areas When,
On the primary surface of the group III nitride crystal substrate, by contacting the solution of a nitrogen-containing gas in a solvent containing a group III metal and an alkali metal, growing said III-nitride crystal on the main surface A process ,
A method for growing a group III nitride crystal, wherein the solvent contains a group III metal having a purity of 99 mol% or more and an alkali metal having a purity of 99 mol% or more . The method for growing a group III nitride crystal according to claim 1, wherein the nitrogen-containing gas is a nitrogen gas having a purity of 99 mol% or more.

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